try with priests: strenght 6 spells are useful against his tanker units. Temple guard with the armour piercing banner should be nice. If your enemy uses khorne, redirect him with skinks. Salamanders on his marauders should do well. If you are desperate you can try a young stegadon: the giant bow doesn't allow the armour save, and the monster will be nice in close combat. Also, NEVER take spears with saurus. Parry saves are much more useful